INTKODVCTOBY ESSAY. 113 time a nearly complete identity of vegetation. Many North African or Arabian forms, such as Peganum Harmala, Fayowa Cretica, Balanites ^Egyptiaca, Acacia Arabica, Alhayi, Gran- ffea, CalotropiSy Salvadora Persica, extend throughout all the drier parts of India. Others have a less extensive range, being only found in Northern and Western India : of these, Malcolmia Africana3 Farsetia, several species of Cleome, Bal- samodendron, Astragalus hamatus and others, Cucumis Colo- Cynthia, Berthelotia, Antickaris Arabica, spinous AcanthaceG, Cometes, Forskalea, Populus Euphratica> Ephedra, Salix dG- gyptiaca, Crypsis, etc. etc., may be mentioned as instances. In India, as in Africa, this peculiar vegetation passes by insen- sible gradations into the European Flora on the one hand, and into the tropical on the other. 7. The Tropical African type. — Though tropical Asia and Africa are separated by a vast expanse of ocean, there is a striking similarity in their vegetation. This is shown not only by the identity of the annual vegetation which springs up during the rainy "season*, but by a great similarity in the families and genera of the frees and shrubs : Capparis, Grewia, Sterculiacea, Tiliacea, columnar Euphorbia, and many other Euphorbiacea, Antidesma, Lepidostachys, Qlatine&9 'Acacia, and Rubiacea, may be mentioned as examples. Too little is known of the African Flora to enable any de- finite conclusions to be drawn as to the numerical value of this type in India, but it is evidently an important onet. A curious affinity may also be traced between the mountain vegetation of western tropical Africa and that of the Penin- sular chain., where the absence or comparative rarity of many of the principal features of the Malayan Flora has already * Polani&ia, Gyn<mdropsist Uirenat 8id&9 fflelocMa, Biedteya, Corc7torus9 Triumfetta, JZscfynomene, Smithia, Indigofera, Doliehos, Ammannia, Cucwbi- tace&> JBfamea, Vemonia cinerea, JSxacwm, Scrophulariaeea, Leueat, Ocymwn J&dycMwn, Amomum, Qloriosa, CommetynaceoB, Brasses, and Cyperacea. t The MelicmtTws Emalaycmus, described by Planchon, ia a garden plant, introduced from the Cape of G-ood Hope into the Himalaya, and ia not dis- tinct from the common Cape species.